Electrical transmission system



Aug. 20, 1940. P. H. sMl-TH vEL'CTRLCL TRANSMISSION SYSTEM s sheets-sheet 1 Filed Feb. 9, 1955 Aug. 20, 1940. P, H, sMlTH '2,212,214

ELECTRICAL TRANSMISSION SYSTEM Filed Feb. 9, 1955 l s sheets-smet 2 /NVENTOR BVR/ SM/TH A T TORNEV P. H. SMITH ELECTRICAL TRANSMISSION SYSTEM s sheets-sheet s Filed Feb.v 9, 1935 FIG. 8

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1 =/s METE/es A l2 =24 METERS 1 =a6 METEns A. =ls METERs k s 24 METERS as METERS E /Nl/ENTOR I? H. SMIT/1' A T Tom/Ev Patented Aug. 20, 1940 vUNITED's'rfrl-:fs PATENT OFFICE ELECTRICAL TRANSMISSION SYSTEM Phillip H. Smith, Boonton, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application February 9, 1935, Serial No. 5,694

33 Claims. (Cl. 178-44) This invention relates to electrical transmiscertained in accordance with the method referred sion systems and especially to methods and to above, the network being located nearer the means for preventing wave reection on multitransmitting end of the line and comprising an frequency radio transmissionlines. open-ended lire one-half of the shortest wave- Wave reection which occurs on an open-.ended length long and a, short auxiliary line of critical l line and produces losses and undesired radiation length connected in shunt to the open line at may be suppressed by connecting a pure resistthe mid-point thereof. The network presents a ance equal to the line characteristic impedance large or infinite impedance to the shortest wave across the terminals .of the line. In the case of and functions for this wave as if removed. Re-

mi. lines designed for single frequency operation and ection is prevented for the wave of longest length terminated in a complex load unequal to the line by means of an auxiliary line network having a characteristic impedance, standing waves resultcritical value and position, this network beingA ing from reection'may be suppressed by means located still nearer to the transmitter and having of an impedance transformer which' changes the an infinite impedance for waves of the' shortest g5 load impedance into the line characteristic imand intermediate wafe-lengths.

pedance. A transformer for satisfactorily match- According to a different embodiment, a multiing a complex load to a line is described in my frequency line is terminated satisfactorily bya, Patent 2,041,378 granted May 19, 1936. In the network comprising two branch lines included in ease of lines terminating in a complex load .and the main line. one of the branch lines including A (i designed for multi-frequency operation, considmeans for terminating the main line at two freerable diilculty has been encountered in supquencies and the other including means for terpressing standing Waves atthe various frequenminating the line at the two remaining frequencies for the reasons, among others, that the cies. Each branch line also includes means for complex load impedance varies with frequency rejecting Waves for Which the line iS terminated 5 and the impedance of the device for suppressing by the other branch line. 2 reflection at one particular frequency often ren- The invention will be more fully ./understood ders the elimination of standing waves at the from the following specication taken in connecother frequencies difficult, tion with the drawing on which like reference It is one object of this invention to suppress characters designate elements of similar funcstanding Waves on a line in a simple and ecotion and on which: 30 nomical manner. Fig. 1 illustrates a two-frequency radio trans- It is another object of this invention to supmission system including a network for Suppresspress on a multi-frequency line standing waves ing standing waves at both frequencies;

at each of the frequencies. Figs. 2, 3, 4, and 5 are curves used in explain- It is a further object of this invention to suping the operation of the system of Fig. 1

press, on amulti-frequency line, standing waves Fig. 6 illustrates a radio transmission system at one frequency without affecting the operation which includes a network for suppressing standof the system at other frequencies. ing waves at each of four frequencies;

According to one embodiment of this invention, Figs. 7, 8, 9, 10, 11, and 12 are curves and diaas incorporated in a high frequency system comgrams useful for explaining the oper-ation of the o prising means for simultaneously or non-slmulsystem of Fig. 6; y taneously supplying three different frequencies Fig. 13 isla perspective end View of a network to an antenna, standing waves are eliminated for which may be substituted for that shown in the the wave of the shortest wave-length by means system illustrated by Fig. 6.

5 of a short auxiliary line connected in shunt to Referring to Fig.- 1, reference numeral I desigthe main line at a point near the antenna. The nates a multi-frequency source of radio frequenexact position of this shunt line with respect to a cy comprising transmitters 2 and 3 which supply current maximum point of this wave, and the two waves having, respectively, a length 7u and length or impedance value of the auxiliary line A a length i2. These transmitters may supply said l, corresponding to this exact position, are de- Waves at the same time or different times and 50 termined in accordance with the method dispreferably include filters for preventing interacclosed in my patent mentioned above. For the tion of the two transmitters. Reference numeral intermediate wave-length reflection is prevented 4 designates a line and numeral 5 a complex load by means of a distributed network having a critiunequal to the characteristic impedance of the l cal position and a critical impedance value as asline. Reference numeral 6 designates an im- E pedance transformer, such as that disclosed in my patent mentioned above, for transforming the load impedance 5 into the characteristic impedance of the line at the frequency corresponding 5 to wave-length M. Reference numeral 1 designates another impedance transformer comprising a short-circuited auxiliary line tapped at intermediate points 8 by the main line 4. This transformer functions to suppress standing waves hav-A 10 ing a frequency corresponding to M and also functions for the wave-length M as if removed from the main line 4.

Considering waves of wave-length M, the impedance transformer 6 has a critical position with' respect to a current maximum point of the stand-` ing wave-length M and a critical value'corresponding to the critical position, the critical value or length l1 and position being determined after determination of the ratio of the current maximum and minimum amplitudes from the curves of A long and therefore not resonant at the frequency corresponding to wave-lengthM.

The method of ascertaining the proper position on transformer 1 of the tapping points 8 for obtaining the value of impedance necessary to suppress standing waves of wave-length M land corresponding to the given position of the trans former 1, will now be explained. The short auxiliary line or transformer 1 may be. viewed as two sections, one o'n each side of the tapping points 8.

The impedance of the closed section may be written Z1=Z0 tanh (ad-l-j) Y (1) 4and the impedance of the open section may be written 5 z2=zo com. a+j 2) these equations being obtained from the textbook by J. A. Fleming entitled The Propagation of Electric Currents in Telephone and Telegraph Conductors,.thi rd edition, pages 81 and 97, where Zo=characteristic impedance of each section Iand main line r=resistance per loop of unit length L=total length of transformer 7v=1 Z2=distancefrom open end to tap points 8 At frequencies but slightly `off resonance, the

parallel resultant, Za, of Z1 and Zzis essentially imaginary, and since the sections are of very low loss or low resistance, this resultant reduces to jZo which is the equation for the curves of Fig. 3. On

Fig. 3 the percentage designations associated with the various curves represent the different percentages of the longer waveflength A2 which the length L of transformer 1 having a length 10 may have. Knowing the characteristic impedance Zo, the actual imaginary impedance' 15 iin: may be determined from Fig. 3 and the relation :tjx

z., K Using the particular curve of Fig. 3 correspond- 20 ing to the known ratio of wave-length M and M, and knowing the critical value of impedance as indicated above, the tapping points 8 on transformer 1 may be ascertained.

In place of transformer 1 a transformer 9 com- 25 prising two open-ended sections may be employed. The parallel resultant of transformer 9, it can be shown, is 30 -jZo Z'Ihn-tan -i-tanl (s) which is the equation for each of the curves of Fig. 4. I

The impedance transformers 1 and 9' function to suppress standing waves as explained above having a wave-length M and function as if removed for wave-length M, as may be seen from the following. At resonance, which occurs when 40 the closedtransformer 1is or an odd multiple thereof and when the open 45 transformer 9 is or a multiple thereof long, the parallel resultant ZS is essentially real in the case of lines of low aty 50 tenuation and may be written, for the closed transformer 1,

The real impedance ZS is a maximum at the open end of the line and varies with frequency. However, for any particular frequency, that is, for constant values of and the impedance looking into the line at an intermediate tapping point is 35 a function only of the attenuation a and a. The attenuations a and a depend upon the position of the tapping points 8. Fig. 5 illustrates the relation between the impedance at an intermediate tapping point and the maximum impedance inthe/70 case of a line short-circuited at one end arid in the case of a line open at both ends. As shownV on the curve of Fig. 5 the impedance Varies from a maximum designatedlOOper cent to zero. The. maximum is a very high value and depends upon 75 M, X3 and M.

the characteristic impedance and the construction of the line. Ordinarily it is Aof the order of several hundred thousand ohms. In the case of the closed transformer it will be seen that the impedance is sufllciently large, except when the tapping point is very near the short circuit, to function as if removed foi` M. In the case of the open line it acts as if removed except when the tapping point is near the center.

Referring to Fig. 6, reference numeral' IQ designates a multi-frequency transmitting rhombic antenna of the typenow well-known in the art.,

This antenna is connected by means of a main transmission line Il to a multi-frequency source I2 'comprising transmitters I3, I4, I5 and I6 for simultaneously or nonsimultaneously supplying,

respectively,` frequencies having wave-lengths v corresponidng to M, M, M `and M. These transmitters are each connected to the main line II through a lter I1 designed to pass only the frequency supplied by the associated transmitter.

'The far end terminals of antenna III are conto suppress, at the respective frequency, standing waves on the antenna and to dissipateenergy.

Connected across the main transmission line I I are four impedance networks 26, 21, 28 a`nd 29 for suppressing standing waves on the main line Il at the frequencies corresponding, respectively, to wave-lengths M, M, M and M. Each transformer has, at the wave-length at which it functions to suppress standing waves, a critical value and a critical position with respect to the current maximum point of the respective standing wave, in accordance with the teaching of my copending application, Each transformer 'or network changes the load impedance, comprising the antenna IIJ and the portionof the line II and associated equipment located betweenthe antenna I' and point of connection of the transformer, into the characteristic impedance of the line. Considering any transformer, the transformer has a large impedance, and so functions as if removed, at the, frequencies at which the line is terminated at points nearer the load or antenna. Thus transformer 21 isanti-resonant at wave-length y M, transformer or network 28 anti-resonant at Thetheory explaining the operation outlined' above of the various transformerswill now be discussed. Transformer 21 comprises an open line, a half wave-length long, at the wave-length M, line 4sections 30 and 3|V eachbeing a quarter wave-length long, at M. This half. wave-length line constitutesfaninflnite impedance, substantially, for Wave-length M and the network 21 therefore functions as if removed for wavelength M'. A short auxiliary line 32 of either adjustable or predetermined length is connected to the midpoint of the half wave-length line just described for the purpose of rendering the impedance of the transformer 21' equal to the Ivalue chosen in accordance with the method described in my copending application. The connection at the midpoint does not affect the operation of the half wave-length line comprising sections 30 and 3i inasmuch as the impedance at the mid-point of the half waverlength is zero at M. For a given known ratio i n i, the relation between the impedance of the transformer 21 at M and the length of the short line 32 may-be calculated, the impedance of sections 30 and 3| being calculated or known at M.

Fig, 7 shows the relation between the impedance looking into an open-circuited line similar to line 32 and thellength in wave-lengths, where i. is the wave-length of the wave supplied tothe line. The actual impedance may be obtained after ascertaining the characteristic impedance Zn of the line from the relation Where K is obtained -from Fig. 7. The curves of Fig. 8 illustrate, each fora dierent ratio of M to M, the relation between the length of adjustable section 32 and the calculated impedance of the network 21. The curves of Figs. 2, 7 and 8 maybe combined for convenience 'as illustrated by the curves of Fig. 9, and the length of section 32 may be quickly determined. Thus referring to Fig. 9 the position of transformer 21 with respect to a given maximum current point may be determined from the known or measured ratio of the current maximum and minimum amplitudes atM, that is Imin A Knowing the ratio and therefore the proper curve of Fig. 9 to use, the length of section 32 may be determined on the vertical scale.

Transformer 28 isin a sense an extension of transformer 21 and is anti-resonant at M and M. This transformer includes in effect an open half wave-length line at M, sections 30 and 3l. It

also includes an open half wave-length line at M,

section 33 being a quarter wave-length long at M and sections 30, 3i and 34 constituting electrically a quarter wave-length line at M. The adjusted, or predetermined, length of section 35 is such as to render the impedance of the network 28 equal to the value necessary to suppress standing waves at M on main line II.` It is believed to be apparent that transformer 29 includes an open half wave line at M, an open half wave line at M, and in addition an open half wave line at M, section 36 being a quarter wave-length long at M, and

sections 30, 3|, 33, 34, and 31 being electrically equivalent to a quarter wave-length line at M. The length of sectionv38 is such as to render the impedance of the, network 2'9 equal to' the previously determined critical value for suppressing standing waves on main line Il at M.

Referring to Fig. 10 the method of determining the length of section 34 of transformer28 will non. be explained. In the first place the length ci the section 35 may be disregarded inasmuch as it is in shunt with a zero impedance point on a half wave-length line at M. The physical lengths of all the other sections of the network, except section 34, are easily determined since the actual wave-lengths M and M are known, these known lengths being expressed in terms of wave-length M. The problem is therefore reduced to a determination of the parallel impedances X1 and X2 which when combined with the former 28 at M. The length 2 u minus the length of section 38 at determines the length whose reactance, let us say, is X1. Reactance X3 may be determined so from'Fig. 7. Now.

is the length of section 3| expressed as a fractional part of the wave-length lat M. X2 is, therefore,`readily obtainable and is l 7 length at M.

Transformer 28 has an input reactance Xs at M which is controllable 'by means of the adjustable section 35 between plus and minusinfmity neu'glecting losses. In practice it appears that a impedance of section 30 at M anti-resonate trans! are expressed as a fractional part of a Wavecut and try method of adjusting this length is satisfactory. It may be calculated as follows:

Referring to Fig. 10 all dimensions except the length of section 35, which has a reactance Xs. of the network i8k are known and may be expressed in terms of M. The input reactance indicated as Xe at M is:

the correct algebraic sign being applied to the reactances. For a given adjustment of section 35, X4 and X5 are computed at M from Fig. '7. A particular length of open-circuited transmission line in terms of M may next be found vhaving the same reactance as Xe by means of Fig. 7. This new representative length when added to the length of section 34 permits the computation of reactance X2 from Fig. 7. X2 is then combined with X1 and the resulting reactance is also represented by a line of length which may be readily calculated from Fig. '1. This second representative length when added to the length of section allows the calculation of the input reactance of the whole network 28.

If the reactance of the network 28 be computed for aseries of lengths of the adjustable element 35, a smooth curve may be plotted to show the input reactance of transformer 28 as a function of the length of the adjustable section for a fixed set of wave-lengths M, M and M. Knowing the desired value of network impedance Xs according to the method of my copending application, the length of the adjustable section-35 may be ascertained from the curve. Fig. 11 i1- lustrates the curve obtained when M- equals 16 meters, M equals 24 meters and M equals 36 meters; and Fig. 12 illustrates the actual arrangement when these wave-lengths are employed.

It is believed to be apparent that, in accordance with the method described above, the length of section 31 of transformer 29 may be ascertained and also the length of the adjustable section 38.

Referring to Fig. 13 a perspective end view of a four-frequency network is illustrated, which network may be substituted for the equipment shown included between the line XX and YY of f Fig. 6. In the system of Fig. 13, liranchlines` 39 and 40 are inserted in the main line Il. As `in the system of Fig. 1, in branch line 39, trans-v formers 4 and 42 function to suppress standing waves having a wave-length M and M, respectively; and in branch line 40, transformers 43 and 44 suppress standing waves having a wave-length of M and M, respectively. Transformers 42 and 44 are anti-resonant, respectively, at M and M since they constitute closed auxiliary lines a quarter wave-length long at these respective wavelengths.

The auxiliary line 45 having a length equal to one-quarter of M and located at a distance of one-quarter of M from -junction 46'offers an infinite impedance to waves' having a wave-length of M.- Auxiliary line 41 is similarly dimensioned and similarly positioned with respect to junction 48 and: blocks the flow of waves of wave-length M. Auxiliary lines 49 and 50, each having a length of Y and located at a distance of one-quartei` of M from junctions 46 and' 48, respectively, function to keep waves of M from entering the line 39. The Vclosed line comprising sections 4,9 and 5I and the Vclosed line comprising sections 50 and 52, each constitute an infinite impedance at M inasmuch as they are each one-quarter of a wavelength at M. The transformers and 49, 5I

leach produce a disturbance or standing waves at lengths M and transformers 51 and 58 function to block M, as indicated by the dimensions of these transformers. The shorted line comprising section 51 and 59 and the shorted line comprising sections 58 and 60 function as if removed for M. y Transformer 6I functions to suppress the standing wave set up by transformers 55 and 51, 59 at M and transformer 62 functions to suppress the standing wave produced at M byu transformers 55 and 51, 59. Y l

i Although the invention has been described in connection with certain embodiments and ap paratus, it is understood that it is not to be limited to i such embodiments and apparatus. Obviously different apparatus may be employed for` suppressing standing waves on a line at a number of different frequencies in accordance with `the invention.

What is claimedis:

`1. A method of suppressing standing waves on a radio transmission path between a source and a load at a plurality of frequencies, which comprises transforming for one frequency the load impedance into the characteristic impedance of the path at one point in said path, similarly transforming the load impedance for. another frequency at a point nearer the source in the same path, and preventing at the last-mentioned point reflection atthe first-mentioned frequency.

2. A method vof matching at a plurality of frequencies a 1oad impedance`and the impedance of the associated line .connected to a multi-frequency source, utilizing a plurality of reactive devices, which comprises matching at a flrst point on the line the load and line impedances for a first frequency, connecting to the line at a second point nearer the source a-particular reactive device having an infinite impedance valuefat the rst frequency, and adjusting said particular device to match the load and line impedance for the second frequency. y

v3. In a radio system, an antenna adapted to operate on a plurality of frequencies and a trans- Vlation device, a transmission line connected therebetween, said line over a portion of its length being divided into parallel paths each for a different plurality of operating frequencies, andl means in each path for matching the antenna impedance andthe line characteristic impedance for the frequencies corresponding to that path 4. In aradio transmission system, a line connecting a multi-frequency source to a load, a shunt impedance for suppressing a. standing wave .y of a given frequency connected to said 4line and having a value dependent upon the ratio of the current maximum to the current minimum of said. standing wave, another shunt .impedance for suppressing a standing wave of a lower frequency connected across the line at a point nearer the source and having a value dependent upon the ratio of the current maximum to the current minimum ofthe wave of said lower frequency, said last mentioned shunt impedance having a large impedance at the rst mentioned given frequency.

5. In a radio transmission system, a single path connecting a multi-frequency source to a load, and a plurality of impedances each for transforming at a different one of the transmitted frequencies the load impedance into the characteristic impedance of the path, at least one of said impedances having an innite impedance value for al1 the transmitted frequencies except that at which it functions to match the load and ,line impedances.

6. In a radio transmission system, a single path connecting a ,multi-frequency source to a complex load impedance unequal to the characteristic impedance of the path and means comprising a portion of said path and at least one impedance connected in shunt to said path at an intermediate point thereof for suppressing standing waves produced by said load at the,"

transmitted frequencies.'

7. In a radio transmission system, a line connecting a multi-frequency source to a load, impedance means connected in shunt to said line for suppressing standing waves at oney of the frequencies transmitted, a second impedance means connected in shunt to said line at a point nearer said source for suppressing standing waves at 'a' frequency lower than the first mentioned frequency, said second means having a relatively large impedance at said -first mentioned frequency.

8. In a radio transmission system, a line connecting a multi-frequency so'urce of radio energy toy a load, impedances connected to different points of said line, each for suppressing ata different frequency standing waves on the line between said source and the point of connection for said impedance, each impedance being anti-` resonant at the frequencies at which standing wavesare suppressed by means of impedances located nearer the load. v

9. In a radio system, a plurality of sources for supplying currents of different frequencies, a load, a line connecting said sources to said load,

a shunt impedance for suppressing standing waves at a given frequency connected across the line and having a value and position de- ;pendent upon the ratio of the maximum and minimum amplitudes of the standingwaves at said frequency, a second shunt impedance l connected acrossjthe line at a point nearer said source for suppressing standing waves at a lower frequency and having a value at the lower frequency and a position dependent upon the ratio Yof the maximum and minimum amplitudes of the standing wave at said lower frequency, the second impedance being anti-resonant at the first mentioned frequency. y

10. In a radio transmission system, means for supplying two currents of different wave-length, a load, a main line connectingsaid means and load, an auxiliary line impedance for suppressing the standing wave` of the shorter wave-length connected in shunt to said main line at a point less than one-eighth of said wave-length froma maximum current point of said wave, a second auxiliary line impedance for suppressing the standing wave of thelonger wave-length having a length equal to `one-quarter or a multiple thereof of the shorter wave-length, said auxiliary line being connected at an intermediate point thereof in shunt to the main line at a point on said main line nearer said means and less than 'one-eighth of the longer wave from a maximum main line at a point less than one-eighth of said wave-length from a maximum current point of said standing wave, a second distributed impedance for suppressing a standing wave having a longer wave-length connected to said main line at a point nearer said means and less than oneeighth of said longer Wave-length from a maximum current point of the standing wave of longer wave-length, said second impedance comprising an open line having aV length equal to one-half or an odd multiple thereof of said shorter wavelength and a line connected to the mid-point of said open line, the length of said `last mentioned iine being dependent upon the ratio of the two Wave-lengths. i

12. A radio transmission system in accordance With clain 11, a shunt distributed impedance for suppressing a standing wave having the longest wave-length connected to said main line at a point still nearer the said means and less than one-eighth of said last mentioned wave-length from a maximum current point of said longest wave, said shunt impedance .being anti-resonant at frequencies corresponding to said shortest and longest wave-lengths.

.13. In a radio system,Y a main line, a multi-frequency source, a complex load having an impedance unequal to that of said main line, a plurality of branch lines each connected between said load and included in said main line, and meanslineluded in each branch line for suppressing at more than one of the transmitted frequencies standing waves produced by Waves traveling on the Ibranch line. T y

14. In a radio system, a main line connecting a multi-frequency source to a load impedance,

branch lines included insaid main line, transforming means comprising distributed impedance included in each branch line for transforming at two frequencies the load impedance into the line characteristic impedance, filtering means comprising distributed impedance included in each branch line for preventing the now of current of the remaining frequencies, and impedance means included in each branch line for eliminating at the two rst mentioned frequencies the effect of said filtering means.

r 15. Ina radio system, a main line connecting a source for supplying current of source for supplying current frequencies f1, f2, f3 and f4 to a load, two branch lines included in said main line, means included in one branch line for preventing the flow of current of frequencies fi and fz and for suppressing standingv waves on said main line having frequencies fs and'f4, and means included in the other branch line for preventing the iiow of current having frequencies ,f3 and f4 .and for suppressing standing waves having frequencies f1 and f2.

16. In combination, a transmission line, means for impressing alternating currents of a plurality of predetermined frequencies on said line, a load connected with the end of said line, means for load connected with the end of said line, means for matching the load impedance to the surge impedance at all and any one of said frequencies without impeding the passage of Acurrents of said frequencies through the line, the. impedance matching means consisting solely of fixed impedance devices permanently bridged across the line, portions of the line conductors between impedance device junctions therewithY and the load, and a fixed impedance device permanently bridged across a portion of at least one of said impedance devices.

18. In combination, a transmission line, means for impressing alternating currents of a plurality of predetermined frequencies'on said line, a load connected with the end of said line, means for matching the load impedance to the 'surge impedance at all and any one of said frequencies without impeding the passage of currents of said frequencies through the line, the impedance matching means consisting solely of wire networks permanently bridged across the line, and portions of the line conductors between network juctions therewith and the load.

19. In combination, a trasmission line, means for impressing alternating currents of a plurality of frequencies on said line, and a plurality of fixed impedance devices permanently bridged across the line and so proportioned that they present substantially infinite impedance, each at a dinerent frequency.

20. In combination, a transmission line, means for impressing high frequency alternating currents of two predetermined frequencies on one end of said line, a load connected with the other end of said line, means for matching the load impedance to the surge impedance at both and either one of said frequencies without impeding the passage of currents of said frequencies through the line, the impedance matching means consisting of two units each consisting solely of a.

fixed impedance device permanently bridged across the line and the line conductors between the junction of the impedancedevice therewith and the load.

21. In combination, a transmission line, means for impressing high frequency alternating currents of a plurality of predetermined frequencies on one end of said line, a load connected with the other end of said line, means for matching the load impedance to the surge impedance at all and any one of said frequencies without impeding the passage of currents of 4said frequencies through the line, the impedance matching means consisting solely oi a fixed impedance device for each frequency permanently bridged across the line and the line conductors between the junction of each impedance device with the line and the load, and an increasing number of impedance elements bridged across a portion of each different impedance device, none across the first, one across the second, two across the third, three across the fourth.

22. In combination, a transmission line, means for impressing alternating currents of a plurality of predetermined frequencies on said line, a load connected with the end of said line, means for matching the load impedance to the surge impedance at all and any one of said frequencies without impeding the passage of currents of said frequencies through the line, the impedance matching means consisting solely of a fixed impedance device for each frequency permanently bridged across the line and line conductors between the junction of each impedance device therewith and the load.

23. In combination, a transmission line, means for impressing alternating currents of a plurality of predetermined frequencies on one endf of said line, a load connnected with the other end of said line, means for matching the` load impedance to the surge impedance at all and any one of said frequencies without impeding the passage of currents of said frequencies through the line, the impedance matching means consisting solely of xed impedance device for each frequency permanently bridged across the line and line conductors between the junction of each impedance device therewith and the load, each impedance device being substantially infinite at another frequency than its matching frequency.

24. In combination, a transmission line, means f or impressing alternating currents at a plurality of predetermined frequencies on one end of said line, a load connected with the other end of said line, means for matching the load impedance to the surge impedance at all and any of said yfrequencies without irnpeding the passage of currents of said frequencies through the line, the impedance matching means consisting solely of a pair of straight conductors for each frequency permanently bridged across the line and line lconductors between the junction of each pair of conductors therewith and the load, and impedance devices bridged across certain pairs of conductors.

25. In combination, a transmission line, means i or impressing alternating currents of a plurality o1' predetermined frequencies on one end of said gine, a load connected with the other end of said line, means for matching the load impedance to the surge impedance at all and any one of said frequencies without impeding the passage of currents of said frequencies through the line, the impedance matching means consistingA solely of a pair of straight conductors for each frequency permanently bridged across the lines and the line conductors between the junction of each straight conductor. pair therewith and the load, and conductor loops bridged across certain pairs of straight conductors. f

26. In combination, a'transmission line, means for impressing alternating currents of a plurality `of frequencies on the line, a load connected to the lend of the line, a fixed impedance device permanently bridged across one section of said line substantially matching the load impedance to the surge impedance when current of one frequency is impressed on the line, and presenting substantiallyinnite impedance at the other fre- Vfquency, and a second xed impedance device permanently bridged across another section of said line substantially matching the load irnped- 'ance to the surge impedance when current of another frequency is impressed on the line and presenting substantially infinite impedance at said one frequency.

27. In combination, a two-wiretransmission jline, Imeans for impressing high frequency alternating currents of two frequencies on the line, a load connected to the end of the line, a fixed impedance consisting of a Wire network permanently bridged across one section of said line substantially matching the load impedance to the surge impedance when current of one frequency is impressed on the line, and presenting substantially infinite impedance at the other frequency, and a second.xed impedance also consisting of a wire network permanently bridged across another section of said line substantially matching the load impedance on the line and presenting substantially infinite impedance at said one frequency. l

28. In combination, a transmission line, a plu- `,rality of alternating current devices of different frequencies, connections between said devices and the line, and fixed impedances permanently bridged across said connections, short-circuiting each connection at frequencies other than that of the associated device, and preventing thereflection of waves into the devices.

29. In combination,-a transmissionline, a plurality of sources of alternating current of different frequencies, connections between said sources and the line, a load connected to the end of the line, and fixed impedances permanently bridged across said connections effectively short-circuiting each connection at a frequency other than that of the associated source, and preventing the reflection of waves into the sources.

30. In combination, a high frequency load adapted for operation on a plurality of different frequencies, a transmission line connecting said load to high frequency apparatus, a first reactance permanently bridged across vsaid line f or matching the impedance of 'said line and load for one frequency to be used thereby, and a second reactance permanently bridged across said line and somewhat removed from said ilrst re.

actance for matching the impedance of said system for another frequency, said second reactance being so designed as to present substantially infinite impedance to energy of said first frequency.

3l. In combination, a high frequency load adapted for operation on a plurality of different frequencies, a transmission line connecting said load to high frequency apparatus, a first reactance permanently4 bridged across said line for matching the impedance of said line and load for one frequency to be used thereby, and a second reactance permanently bridged across said line l for onefrequency to be used thereby, and a second reactance permanently bridged acrosssaid line and somewhat removed from said rst reactance for matching the impedance of said system for another frequency, said first reactance being designed to present substantially innite impedance to energyof said other frequency and said second reactance being so designed as to present pedanceLfor suppressing the standing wave of another frequency, each impedance having a4 value related to the ratio of the minimum and maximum amplitudes of the standing Wave suppressed thereby and at least one of the impedances having a substantially infinite impedance value at the frequency at which the other` impedance functions to suppress the standing wave.

PHIILIP H. SMITH` 

